Lock hopper has an entrance valve above the hopper formed air-tightly and an exit valve below the hopper formed air-tightly. In lock hopper, the entrance valve and the exit valve are opened or closed alternately so that both the entrance valve and the exit valve are not in an “open” state simultaneously. As a result, with lock hopper, a granular substance can be transferred from an upper system to a lower system in a state that the flow of gas is blocked between the upper system and the lower system. Here, the upper system and the lower system are systems which conduct the same operation or different operations.
Lock hopper can receive a granular substance from the upper system into the hopper by keeping the entrance valve in an “open” state and the exit valve in a “closed” state. Then, by keeping the entrance valve in a closed state and the exit valve in an open state, the granular substance in the hopper can be discharged to the lower system. Therefore, even when there is a big pressure difference between the upper system and the lower system, the granular substance can be allowed to flow down and be transferred from the upper system to the lower system with hardly being affected by the pressure difference.
Lock hopper is used in supplying coal to a coal gasification furnace or a fuel to a pressurized, fluidized bed boiler. In supplying granular coal to a coal gasification furnace, the granular coal is transferred from an upper system of atmospheric pressure to a lower system having a pressure of about 30 kg/cm2. In the transfer of coal, coal of an amount of, for example, the full capacity of hopper is transferred periodically.
There is described, in Patent Literature 1, a dry type, exhaust gas treatment apparatus for conducting an exhaust gas treatment using a granular adsorbent. This treatment apparatus uses a lock hopper. The schematic constitution of this treatment apparatus is shown in FIG. 3. Inside an adsorption tower 20, there is formed a moving bed in which an adsorbent (not shown) is transferred from above to below. An exhaust gas G1 is passed through the moving bed, whereby the harmful substance in the exhaust gas G1 is adsorbed and removed by the adsorbent.
An upper lock hopper 15 is fitted above the adsorption tower 20. An adsorbent is fed into the adsorption tower 20 via the upper lock hopper 15. A lower lock hopper 16 is fitted below the adsorption tower 20. The adsorbent having a harmful substance adsorbed thereon is discharged outside from the adsorption tower 20 via the lower lock hopper 16.
Incidentally, in FIG. 3, LS is a level meter; 70 is a regeneration tower; 72 is a sieve; and G2 and G3 are each a gas.
The lower hopper 16 comprises a hopper A3, an entrance valve A1 provided above the hopper A3, and an exit valve A4 provided below the hopper A3. The adsorbent in the adsorption tower 20 is supplied quantitatively into the hopper A3 by a metering feeder 40.
The adsorbent supplied into the hopper A3 is quantitatively discharged from the hopper A3 by a metering feeder 50. A gas G3 is supplied into the hopper A3 through a gas-introducing valve A6 and is discharged outside through a gas-discharging valve A8. By introducing the dried gas G3 (e.g. nitrogen) into the hopper A3, the hopper A3 inside can be kept in a dry atmosphere.
The lower lock hopper 16 can intermittently discharge the adsorbent outside from the adsorption tower 20 by repeating the following three steps (1), (2) and (3).
(1) The entrance valve A1 is set at “open”, the exit valve A4 is set at “closed”, the metering feeder 40 is set at “operation”, and the metering feeder 50 is set at “stop”. By this setting, the adsorbent is discharged from the adsorption tower 20 into the hopper A3.
(2) The entrance valve A1 is set at “closed”, the exit valve A4 is set at “closed”, the metering feeder 40 is set at “stop”, and the metering feeder 50 is set at “stop”. In this state, a gas G4 is passed through the hopper A3, whereby the hopper A3 inside is put in a dry state.
(3) The entrance valve A1 is set at “closed”, the exit valve A4 is set at “open”, the metering feeder 40 is set at “stop”, and the metering feeder 50 is set at “operation”. By this setting, the adsorbent in the hopper A3 is discharged onto a conveyor 60.
The upper hopper 15 comprises a hopper A3, an entrance valve A1 provided above the hopper A3, and an exit valve A4 provided below the hopper A3. An adsorbent carried by an upper conveyor 30 is quantitatively supplied into the hopper A3. An adsorbent in the hopper A3 is periodically discharged into the adsorption tower 20 through the exit valve A4.
As in the case of the lower lock hopper 16, the hopper A3 comprises a gas-introducing valve A6 and a gas-discharging valve A8. By introducing a gas G3 (e.g. nitrogen) into the hopper A3 through the gas-introducing valve A6, the hopper A3 inside can be kept in a dry atmosphere.
The upper lock hopper 15 can periodically supply the adsorbent into the adsorption tower 20 by repeating the following three steps.
(1) The entrance valve A1 is set at “open”, the exit valve A4 is set at “closed”, and the conveyor 30 is operated. By this setting, the adsorbent is supplied into the hopper A3.
(2) The entrance valve A1 is set at “closed”, the exit valve A4 is set at “closed”, and the conveyor 30 is set at “stop”. A gas G3 is supplied into the hopper A3, whereby the hopper A3 inside is put in a dry state.
(3) The entrance valve A1 is set at “closed”, the exit valve A4 is set at “open”, and the conveyor 30 is set at “stop”. By this setting, the adsorbent in the hopper A3 is supplied into the adsorption tower 20.
Patent Literature 1 also describes other dry type, exhaust gas treatment apparatus shown in FIG. 4. An upper lock hopper 17 shown in FIG. 4 comprises a lock hopper E and a lock hopper F, arranged side by side. The lock hopper E comprises a hopper A3, an entrance valve A1 and an exit valve A4. The lock hopper F comprises a hopper B3, an entrance valve B1 and an exit valve B4. This upper lock hopper 17 is constituted so that an adsorbent can be transferred downward continuously by using the lock hopper E and the lock hopper F alternately.
A lower lock hopper 18 is constituted in the same manner as the upper lock hopper 17.
No in-depth explanation is given in Patent Literature 1 but the rough function can be conjectured.
Meanwhile, the present inventors made an investigation on the performance of a practical, dry type, exhaust gas treatment apparatus comprising a continuous lock hopper such as mentioned above. As a result, the present inventors found that there was a big difference in flow amount of adsorbent between when an adsorbent is supplied into a hopper and when the adsorbent is discharged from the hopper. That is, it was confirmed that, when the adsorbent was discharged from the hopper, the flow of adsorbent was low, resulting in the significant reduction in flow amount of adsorbent.
Further, when the dry type, exhaust gas treatment apparatus is operated for many hours, the adsorbent undergoes abrasion and is broken depending upon the operation hour, resulting in a decrease in average particle diameter. In this case, the flow amount of adsorbent decreases further. As a result, a relation of (amount supplied into hopper)=(amount discharged from hopper) does not hold, making the lock hopper system non-operable.
In the above practical, dry type, exhaust gas treatment apparatus, the flow amount of the adsorbent was 24 m3/h and the inner diameter of the exit chute was about 150 mm. Easy flow of the adsorbent discharged is achieved by larger inner diameter of exit chute; however, it makes larger the size of exit valve, etc. Consequently, the construction cost of dry type, exhaust gas treatment apparatus and the maintenance cost thereof increase.
Hence, there is desired a lock hopper which is compact and can secure a sufficient transfer amount of adsorbent.
Patent Literature 1: JP-A-1999-137945